This invention relates generally to digital imaging, and more particularly to x-ray detector imaging.
Radiation imagers, such as digital x-ray imagers, typically include a scintillator coupled to a photosensor array. The radiation to be detected, x-rays for example, are absorbed by the scintillator material with the release of electrons which are converted to optical photons inside the scintillator that in-turn are detected by photodiodes which accumulate charge corresponding with the incident photons. The charge is read out by drive electronics to provide electrical signals corresponding to the radiation image. The data embodied in such electrical signals can be presented in a visual display or otherwise processed to allow analysis of the radiation pattern.
Optimal array performance depends on, among other things, good adhesion between the scintillator layer and the underlying photosensor array. When CsI is evaporated on the surface of a passivation layer, for example, thermal expansion results in forces that tend to peel the CsI layer from the surface of the passivation layer over the photosensor array. As a result, attempts have been made to increase the adhesion of evaporated CsI to a photosensor array; approaches include etching the surface of the underlying passivation layer, typically comprising of Si3N4 (generally referred to as SiN), or adding a buffer layer of polyimide over the photosensor array. While these attempts have been successful within certain temperature ranges, adhesion problems begin to develop at extreme temperature ranges beyond xe2x88x9220 degrees Celsius to +70 degrees Celsius.
There are a number of factors that affect the reliability of the adhesion between CsI and the substrate. For example, a large stress on the CsI-substrate interface may result because of the difference in coefficient of thermal expansion between CsI (typically having a large thickness of 100 to 600 microns(xcexcm)) and the imager glass substrate. Attempts to structure the surface under the CsI layer have consisted, for example, of depositing a thick (xcx9c5 xcexcm) polyimide layer over the photodiode to form a platform on which the CsI is deposited; nevertheless, such attempts have not always provided the desired level of adhesion.
Accordingly, there is a need in the art for a radiation imager having good adhesion between the scintillator and photodiode array.
The present invention provides a process and apparatus for forming a high integrity imager device having a passivation layer disposed over a photosensor array, a passivation layer with an adhesion topography on its surface, and a scintillator layer disposed over the passivation layer such that the scintillator layer is coupled to the adhesion topography.